An organic thin-film solar cell is full of flexibility and can turn into a large area as a whole and be lightweight, and thus it is expected that an organic thin-film solar cell is fabricated with ease and at low cost. Hence, organic thin-film solar cells are considered to be promising next generation solar cells. Improving the conversion efficiency to a significant level is presently an important goal to achieve the practical use of organic thin-film solar cells.
As the structure of an organic thin-film solar cell, bulk heterojunction by a mixture of a p-type semiconductor (electro donor) and an n-type semiconductor (electron acceptor, e.g., C60 derivative) is known. An advantage of the bulk heterojunction is that photoinduced charge separation occurs efficiently due to a large interface between the p-type semiconductor and the n-type semiconductor, allowing a photocurrent to be increased compared to a double-layer solar cell.
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